This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
Use of any of these functions is unspecified in a multi-threaded
The sighold(), sigignore(), sigpause(), sigrelse(), and sigset()
functions provide simplified signal management.
The sigset() function shall modify signal dispositions. The sig
argument specifies the signal, which may be any signal except SIGKILL
and SIGSTOP. The disp argument specifies the signal's disposition,
which may be SIG_DFL, SIG_IGN, or the address of a signal handler. If
sigset() is used, and disp is the address of a signal handler, the
system shall add sig to the signal mask of the calling process before
executing the signal handler; when the signal handler returns, the
system shall restore the signal mask of the calling process to its
state prior to the delivery of the signal. In addition, if sigset()
is used, and disp is equal to SIG_HOLD, sig shall be added to the
signal mask of the calling process and sig's disposition shall remain
unchanged. If sigset() is used, and disp is not equal to SIG_HOLD,
sig shall be removed from the signal mask of the calling process.
The sighold() function shall add sig to the signal mask of the
The sigrelse() function shall remove sig from the signal mask of the
The sigignore() function shall set the disposition of sig to SIG_IGN.
The sigpause() function shall remove sig from the signal mask of the
calling process and suspend the calling process until a signal is
received. The sigpause() function shall restore the signal mask of
the process to its original state before returning.
If the action for the SIGCHLD signal is set to SIG_IGN, child
processes of the calling processes shall not be transformed into
zombie processes when they terminate. If the calling process
subsequently waits for its children, and the process has no unwaited-
for children that were transformed into zombie processes, it shall
block until all of its children terminate, and wait(), waitid(), and
waitpid() shall fail and set errno to [ECHILD].
Upon successful completion, sigset() shall return SIG_HOLD if the
signal had been blocked and the signal's previous disposition if it
had not been blocked. Otherwise, SIG_ERR shall be returned and errno
set to indicate the error.
The sigpause() function shall suspend execution of the thread until a
signal is received, whereupon it shall return −1 and set errno to
For all other functions, upon successful completion, 0 shall be
returned. Otherwise, −1 shall be returned and errno set to indicate
These functions shall fail if:
EINVAL The sig argument is an illegal signal number.
The sigset() and sigignore() functions shall fail if:
EINVAL An attempt is made to catch a signal that cannot be caught, or
to ignore a signal that cannot be ignored.
The following sections are informative.
The sigaction() function provides a more comprehensive and reliable
mechanism for controlling signals; new applications should use the
sigaction() function instead of the obsolescent sigset() function.
The sighold() function, in conjunction with sigrelse() or sigpause(),
may be used to establish critical regions of code that require the
delivery of a signal to be temporarily deferred. For broader
portability, the pthread_sigmask() or sigprocmask() functions should
be used instead of the obsolescent sighold() and sigrelse()
For broader portability, the sigsuspend() function should be used
instead of the obsolescent sigpause() function.
Each of these historic functions has a direct analog in the other
functions which are required to be per-thread and thread-safe (aside
from sigprocmask(), which is replaced by pthread_sigmask()). The
sigset() function can be implemented as a simple wrapper for
sigaction(). The sighold() function is equivalent to sigprocmask()
or pthread_sigmask() with SIG_BLOCK set. The sigignore() function is
equivalent to sigaction() with SIG_IGN set. The sigpause() function
is equivalent to sigsuspend(). The sigrelse() function is equivalent
to sigprocmask() or pthread_sigmask() with SIG_UNBLOCK set.
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
IEEE/The Open Group 2013 SIGHOLD(3P)